Large aperture seven-lens objective lens system



'SR' @man June 24, 1969 ToMoKA'zu KAzAMAKl ETAL 3,451,745'

LARGE APERTURE SEVEN-'LENS OBJECTIVE LENS SYSTEM Filed Feb. 2s, 196eQEGR. vm

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' IN VENTO n www M ma m mn Mazzi i United States PatentOHce N l PatentedJune Z4, 1969 U.S. Cl. 350-176 1 Claim ABSTRACT oFpTHEDIscLosURE A largeaperture objective lens system of focallength F includes sevensuccessive lenses dimensioned and related to satisfy the followingconditions:

wherein F1, 2 n is the focal length of the first to the nth lens, l isthe length of the lens system 'and the confronting faces of the fourthand fifth lenses are joined to form a unit surface.

The present invention relates generally to improvements in lens systemsand it relates particularly to an improved photographic objective lenssystem of large aperture.

Photographic objective lens systems of known Gaussion design, althoughthey have been commonly employed, possess, with other conventionalobjective lens systems of wide aperture, many drawbacks anddisadvantages. While in the Gaussion design lens systems o f smallaperture the aberrations are fairly well compensated, in lenses of largeaperture great ditliculties are encountered in balancing the aberrationsincluding theresidual coma. An increase in coma aberration isexperienced with an increase in lens aperture and it has been a problemof long 4standing to eliminate such coma aberration increase with anincrease in lens aperture.

It is, therefore, a principal object of the present inven-4 tion toprovide an improved optical lens system.

Another object of the present invention is to provide an improvedphotographic objective lens system.

Still another object of the present invention is to provide an improvedlarge aperture photographic lens system in which the aberrations arehighly corrected.

A further object of the present invention is to provide an improvedlarge aperture photographic objective lens system of low residual comaaberration.

Still a further object of the present invention is to provide a largeaperture photographic objectivelens system of the above naturecharacterized vby its high definition, flexibility, and adaptability,

The above and other objects of thepresent invention will become apparentfrom a reading of the following description taken in conjunction withthe accompanying drawing, wherein:

FIGUREl 1 is a longitudinal sectional view of a photographic objectivelensA system embodying the present invention, and

FIGURES 2(a), 2(b), 2(c) and 2(d) are sets of curves illustrating thespherical aberration and sine condition, the chromatic sphericalaberration, the distortion, and the astigmatism of a lens system ofFIGURE 1.

In a sense, the present invention contemplates the provision of anobjective lens system of focal length F containing seven successivelypositioned lenses wherein the index of refraction of each of the first,second, fifth, sixth and seventh lenses is 1.75 to 1.85; the index ofrefraction of the third lens is 1.65 to 1.75; the index of refraction ofthe fourth lens is 1.58 to 1.75, the focal length of the first andsecond lenses is at least equal to F/ 1.55; the focal length of thefirst through the third lenses does not exceed F/ 0.32; the focal lengthof the first through the fifth lens is at least equal to F/0.35; thefocal length of the first through the sixth lens is F/O.5 to F/0.65; theindex of refraction of the fourth lens divided by the index ofrefraction of the fifth lens is 0.85 to 0.98; the

. radius of curvature of the rear face of the third lens is cus lenseshaving front faces of greater curvature than Y the 'rear faces, thethird lens is a negative menscus lens with a rear face of greatercurvature, the fourth lens is a concave menscus lens and the fifth lensis a double f convex lens and cementedto the fourth lens along matingfaces to form a unit or group, and the sixth and seventh lenses arepositive.

Referring now to the drawing which illustrates a preferred embodiment ofthe presentinvention, the improved lens system consists of seven lensesforming six groups,

compensated as to be mutually highly balanced and the Y increase in comaaberration normally experienced with increased aperture is minimized oreliminated.

The improved lens system is a modification of the Gaussion design andincludes first and second lenses 1 and 2, respectively, each of which isof a convex menscus type, having a front face, that is, a face directedtoward the object to be photographed of greater curvature than therespective rear face thereof. The third lens 3 is negaf tive and ofconcave meniscus type and is somewhat spaced from the second lens 2 andits front face is of larger curvature than its rear face. Following thethird lens 3 isv arranged a fourth lens 4 of a concave meniscus type, adiaphragm being positioned between the third and fourth lenses. Thefifth lens 5 is of double-convex type and is cemented to the fourth lens4 along confronting mating faces to form a. unit group. The sixth lens 6may be of double-convex, plano-convex or convex meniscus type with itslarge curvature surface directed rearwardly. The seventh lens 7 ispositive and of convex type. Thus the lens system consists of sevenlenses forming six groups, the lense 4 and 5 constituting a singlelgroup.

It has been found that in the above described lens system theaberrations are compensated with excellent balance, one against theother, under the following parameters and relationships;

the fourth and fifth lenses is considered a unit surface` j and isdesignated as the 8th face or surface,

The condition 1.75N1, N2, N5, N6, N'LSS together with the conditionsFMF/ 1.55, F1 2 3F/0.32 and 0.4Fr60-3F renders the Petzval sum highlysuitable for aberration balance.V The condition 1.65N31.75 inassociation with the condition OAFrOFis effective in preventing anincrease in coma aberration. In a similar manner, the condition1.58N41.75 in association with the conditions 0.98N4/N505 and 0.8Fr83.5Fserves to prevent an increase in coma aberration in the intermediateimage angle area 'Further thel condition 1.58N41.75 in association withthe aforementioned condition 1.75N1, N2, N5, N6, N7; 1.85 preventsexcessive compensation of spherical aberration of a higher order.

Selection of the focal length Fm of the first to the Second lenses andthe focal length FLM of the rst to the third lenses in relation to thewhole resultant focal length F so as to satisfy the conditions FMF/ 1.55and FlgF/OZ provides an adjustment of the Petzval sum and furtherassures the condition OAFrSOF. The conditions F1 2 3 4,5F/0.35 andprovide suitable power to the convex lenses arranged behind thediaphragm so as to prevent any excessive increase m aberration.

The regulating conditions 0.85FlLZF makes it posi objective lens systemaccording to the present invention having a focal length of mm. and arelative aperture of 1:1.2:

The designations d1, d2, du indicate the axial distances betweensuccessive lens faces and correspond respectively to the axial lensthicknesses and the axial spacing between confronting faces ofsuccessive lenses, Nd indicates the refractive indices of the d-line,and vd indicates the Abbe number of the d-line, linear dimensions beinggiven in millimeters. l

The Seidel coefficients of the above example areasv follows:

In the above table, S1 indicates the spherical aberration, S2 the coma,S3 the astigmatism, P the Petzval sum, and S5 the distortion.

As can be seen from the above table of Seidel coeflicients and theaberration curves of FIGURES 2(a) to 2(d) a highly improved photographicobjective lens system is achieved which is superior to and avoids thedrawbacks of the conventional Gaussion design and other design lenssystems of large aperture. The lens system of 'the above example has animage angle of 42 degrees,

and the aberrations are highly compensated to provide Thickness andLenses Radi! separations Ns/ud T1= LIOOOOF L1 d1=.1000F 1. 80416/46. 6 5

dz= .0020F n .51600F L; d3= .1450F 1. 79446/45. 4

d4=.0350F f5 1. 1900015l 1 O L3 ds= .0300F 1. 71736/29. 5

de= .3250F T1= 365901? L4 dz= .0200F 1. 68893/31. 1

rg 1.31500F L; dg=.2000F 1. 77252/49. 6 15 d= .0020F rw= LOOOOF Ladw=.0850F 1. 77252/49. 6

11= .74352F dn=.0020F nz=1.22000F L1 d= .0950F 1. 77252/49. 6 2()wherein the fourth and fth lenses are cemented to form a unit group at acommon interface designated rm r1 n3 designate the respectivelysubscriptedradii of curvature of successive lens faces, dl du designatethe successive spacings between adjacent lens faces, and L1 L, designatethe successive lenses, Nd designates the index of refraction of thed-line and vd designates the Abbe member of the d-line.

References Cited UNITED STATES PATENTS 3,012,476 12/1961 Zimmermann eral. 35o-176 JOHN K. CORBIN, Primary Examiner,

1.75$N1, N2, N5, N6, N7,$1.85 1.65$N3$1.75 1.58$N4$1.75 F1,2$F/1.55F1,2,3$F/0.32 F1,2,3,4,5$F/0.35 F/0.65$F1,2,3,4,5,6$F/0.50.98$N4/N5$0.85 0.4F$R6$0.3F 0.8F$R8$3.5F 0.85F$L$1.2F